Following maxillary posterior tooth loss, the maxillary sinus pneumatisizes or expands in every dimension towards the maxilla. As the maxillary bone resorbs, the sinus is enlarged in a coronal, lateral, anterior and posterior direction. This pneumatization, or expansion of the maxillary sinus resulting from maxillary bone resorption, leaves less maxillary bone for a platform on which to place dental implants. If enough maxillary bone has resorbed, placement of a dental implant would penetrate the floor of the sinus and leave the apical portion of the implant exposed in the sinus and, thus, not engaged in bone. This would result in no bony support around that portion of the implant and negate the purpose for dental implant placement as a means of tooth replacement in the posterior maxilla.
In preparation for dental implant placement in the posterior maxilla, the clinician must evaluate the position of the maxillary sinus relative to the remaining maxillary bone and whether bone resorption has occurred to the point of leaving insufficient amounts of bone for implant placement. If it is determined that insufficient bone exists for placement of dental implants due to the expansion of the maxillary sinus, then a sinus elevation and grafting procedure is indicated prior to implant placement.
The prevalent method of sinus elevation and grafting is called the Caldwell-Luc Osteotomy. The procedure involves reflecting a full thickness mucosal flap to expose the lateral wall of the sinus and maxilla. A lateral osteotomy is then prepared in the lateral wall of the maxillary sinus. The osteotomy is rectangular in shape and is cut as deep as the lateral wall of the maxillary sinus until the sinus membrane (Schneiderian membrane) is exposed. The window, or osteotomy, is then carefully tapped medially to allow entry into the sinus cavity. Afterwards, the sinus membrane is gently elevated from the floor and the anterior and posterior walls of the sinus utilizing various blunt dissecting instruments. After the sinus membrane has been elevated and retracted apically and medially, bone is then placed in the area that the sinus membrane has been elevated from. The mucosal flaps are then approximated and sutured.
One of the technical difficulties encountered during this procedure is the inability of the operator to precisely locate the floor of the sinus as he prepares the osteotomy from an antero-posterior direction (along the X-Y axis). Since the floor of the sinus can elevate and descend variably as the osteotomy moves antero-posteriorly, it is impossible to visualize this course. Therefore, the osteotomy is generally prepared in a straight line higher than the highest point of the sinus floor. This guarantees penetration into the sinus floor since an osteotomy that is lower than the sinus floor at any point will simply penetrate into the maxillary bone and not into the sinus cavity. This would require adjustment by expanding the osteotomy superiorly (apically) in order to penetrate the sinus cavity. Obviously, the additional trimming of bone is traumatic and removes bone unnecessarily.
Another error occurs if the osteotomy is placed too superior to the floor of the sinus. Very careful manipulation must then be effected in order to negotiate the remaining lateral wall of the sinus inferior to the osteotomy and to descend below the Schneiderian membrane in order to elevate it from the sinus floor. This technically difficult maneuvering of the instruments along two planes increases the risk of tearing the membrane and thus compromising the outcome of the graft. Otherwise, the osteotomy must be adjusted by expanding in an inferior direction. This would lead to additional trimming of bone and increase the risk of tearing the membrane during the expansion of the osteotomy. It is nearly impossible to visualize the variable course of the sinus floor as the osteotomy progresses antero-posteriorly. This inability to visualize the course of the sinus floor is the first difficulty encountered in the procedure.
Another difficulty encountered is the varying thickness of the lateral wall of the sinus as the osteotomy penetrates it to expose the underlying Schneiderian membrane. The operator must penetrate fully through the lateral wall (X-Z axis) in order to raise the window and elevate the membrane. However, if the osteotomy is prepared too deep, it can tear through the fragile membrane. Therefore, great operator skill is required to visualize the membrane as the osteotomy is prepared through a varying depth of the lateral wall and the membrane is approached.
A further difficulty encountered is the anterior wall of the sinus. Besides the varying depth of the lateral wall, the anterior wall can also vary in course in the Y-X axis (FIG. 2) just as the floor can vary in course in the X-Y axis (FIG. 2) and the lateral wall can vary in thickness in the Y-Z axis (FIG. 3). Since the osteotomy usually is placed in a straight line apico-coronally (vertically), whereas the anterior wall is usually not a straight line, portions of the osteotomy would be too far posterior to the anterior wall. This would require manipulation anteriorly and then laterally to dissect the membrane from the lateral and anterior walls thus increasing the risk of tearing the membrane from the difficult manipulation in two planes. Again, any additional adjustments to the osteotomy would cause unnecessary bone removal and trauma as well as increase the risk of tearing the membrane.
Most of this technique relies on the careful approximation of the outline of the area of the sinus to be grafted. The osteotomy planned should be inside the sinus borders for reasons explained above. Since it is nearly impossible to accurately follow the varying course of the sinus during the osteotomy, inevitably there would be areas that are not exposed by the osteotomy. This would require the careful manipulation of the sinus membrane which risks damage to the membrane. Furthermore, as the lateral wall of the sinus is being cut, the varying thickness of the lateral wall requires that the surgeon proceed very carefully and rely on visual as well as tactile senses to establish that the wall has been pierced without entering the sinus so as to not damage the immediately underlying membrane.
One of the most reliable methods to graph the maxillary sinus in three dimensions is through a computerized axial tomography (CAT or CT) scan that renders the sinus in the X, Y and Z planes. The CT scan can then be formatted for evaluation utilizing three-dimensional (3-D) imaging software. The 3-D imaging software allows the clinician to view the sinus in all dimensions as well as to manipulate the image and prepare a treatment plan as to the location and amount of bone to be grafted in the sinus in order to augment the missing maxillary bone that the sinus has expanded into. This information can then be utilized by the surgeon to establish the parameters of outline and volume of the area of the sinus to be entered for bone grafting.
Even with the information provided by the CT scan utilizing the 3-D imaging software as to the outline of the sinus in the X, Y and Z planes and all other parameters, there has been no mechanism to accurately transfer this highly precise information to the surgical field. Meticulous planning of the parameters of the sinus to be elevated and augmented has been thwarted by the inaccurate approximation in the transfer of this information during the surgical procedure.
There has thus been a gap between the extremely precise diagnostic information and treatment planning obtained by the CT scan and 3-D imaging software, and the accurate transfer of that information into the surgical field to aid the surgeon in executing such a treatment plan.
Accordingly, the objects of the device and method of the present invention are to overcome the limitations and drawbacks of the prior art and provide a significant contribution to the state of the art of reconstructive surgery of the maxillary sinus by providing a surgical guide and bur and a specific method of use wherein the guide has the advantages associated with transferring precise data obtained from a CT scan utilizing 3-D imaging software into the surgical field and aiding the surgeon in such surgery.